In various types of drilling operations, the drill bit is forced downward under pressure while being rotated in order to penetrate earthen formations. These drilling operations can require the application of relatively high downward force to the drill bit as well as relatively high torque to turn the drill bit. One example includes a large drilling rig to which is attached a rotary drive mechanism. Typically, the drill's rotary drive is capable of being raised and lowered along a substantially vertical axis directly above the formation to be drilled. Additionally, a length of drill pipe or drill string is connected to the rotary drive so as to extend downwardly therefrom in a substantially vertical direction. A drill bit is secured to the downward end of the drill pipe.
The drilling rig's rotary drive is activated to rotate both the drill pipe and the drill bit at the suitable speed. Then, the rotary drive, together with the drill pipe and drill bit, is lowered so that the drill bit contacts the surface of the formation to be drilled. Downward pressure is then continuously applied to the rotating drill pipe and bit to force the drill bit to cut downwardly into the formation. As the drilling operation occurs, air is forced through the interior of the rotary drive head, drill pipe, and through the drill bit, thereby forcing cuttings out of the hole and maintaining a clear surface upon which the drill bit may operate. When the drilled hole is deep enough to accommodate the first length of drill pipe, the drill's rotary drive is disconnected from the drill pipe and raised to its original position. A second length of drill pipe is then connected between the rotary drive and the first length of drill pipe. The rotary drive is then activated and the drilling operations are continued. This procedure is repeated until a suitable hole depth is achieved.
In order to reduce problems associated with vibration and shock to the drilling apparatus, various devices have been employed to dampen vibrations and absorb torsional forces during the operation of the rotary drill. These devices typically comprise a force absorbing apparatus which is connected between the drill machine's rotary drive head and the drill pipe. In some instances, the force absorbing device includes some type of resilient, or elastomeric, material which absorbs the vibrations and shocks, thereby dissipating the undesirable energy associated with the drilling operation.
Vibration dampeners or shock absorbers have been characterized by short operating lives. Some designs use an elastomeric cushion to absorb the vibrational effects of the drilling process, combined with positive stops that limit deflection of the elastomeric cushion. While effective, these products have a relatively short wear life. As the shock absorbing elastomeric cushion wears, the positive stops are subjected to increased forces. This may wear or damage the shock absorber in any of a number of locations. Damaged shock absorbers require removal from the drill string and replacement, creating work stoppages. In some instances, the shock absorber may be repaired instead of replaced. If the shock absorber is eligible for repair and continued use, it must be serviced. In some instances, this can require a complicated disassembly process.